<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var a=1;
        var a1=2.2;
        var a2 = NaN;

        document.write(a+"<br>");
        document.write(a1+"<br>");
        document.write(a2+"<br>");
        alert("我是你的爸爸")


        //应用类型数据
        var str = "234";
        var str2 = "afb";
        var str3 = 'abc';

        document.write(str+"<br>")
        document.write(str2+ "<br>")
        document.write(str3 + "<br>")

        //boolean 数据类型
        var b1 = true;
        var b2 = false;

        document.write(b1 + '<br>')
        document.write(b2 + "<br");


        //
        var obj = null;
        var obj1 = undefined;
        var obj2 ;
        document.write(obj + "<br>");
        document.write(obj1 + "<br>");

        document.write(obj2 + "<br>");
    </script>
</head>
<body>

</body>
</html>